The proposed research concerns the development of language and gestural communication skills in Autistic and other developmentally disordered children. The specific aims of this study are to address the issues of whether the impaired communication skills of Pervasive Developmental Disorder/not Autistic children and adolescents differ qualitatively or quantitatively (in degree) from those of nonverbal Mental Age and Mean Length of Utterance matched Autistic age-mates and whether Down's Syndrome children and adolescents matched to the above groups on MA and MLU differ from them in basic communication skills. It is hypothesized that the failure of Autistic children to engage in gestural joint attention interactions with caretakers may in part underlie their specific deficit in the use of personal pronouns and their difficulty in using language appropriately in communication. The proposed research will deal with the communicative skills of groups of adolescent (12 - 16) and younger (6 - 11) children who are Autistic, Pervasive Developmental Disorder/not Autistic, or Down's Syndrome. All will be children who have some expressive language. Younger PDD and DS children will be matched to the younger Autistic group on MLU and nonverbal MA. The adolescent PDD and DS groups will be matched to the adolescent Autistic group on nonverbal MA and MLU. Each participant will first be seen for standardized assessment to determine nonverbal MA, language level, adaptive behavior and emotional disturbance or Autistic behaviors. Those meeting specific cutoffs and DSM-III diagnostic criteria for inclusion in the study groups will be seen for videotaping. All participants will then be assessed for ability to produce and respond appropriately to attention-directing gestures and language and to produce particular communicative acts (speech acts) in situations that call for them. Their communicative behaviors during an interaction with a familiar person will also be examined. Adolescents will additionally be assessed for adequacy of conversational responses and awareness of the informational needs of others. Behaviors will be coded from videotapes using well-defined coding systems that capture both qualitative and quantitative aspects of communication and that preserve information about the sequence of events. Information gained from this work will benefit the populations studied by providing better understanding of the social/communicative skills in which they are deficient, as well as providing specific intervention strategies.